This invention relates to a hydraulic servomechanism for a hydraulic servo brake or clutch and more particularly to a loss stroke reducing apparatus for a hydraulic servomechanism capable of reducing the loss stroke of an input shaft in the initial stage of operation.
A hydraulic servomechanism is normally equipped with a power piston slidably fitted in a housing, a power chamber formed at one end of the power piston and a control valve operated interlockingly with an input shaft to make the power piston move forward by introducing hydraulic pressure proportionate to the input applied to the input shaft into the power chamber, whereby the hydraulic pressure proportionate to the input introduced into the power chamber is used to boost a small input and convert the input to a boosted output.
Although the control valve is designed to connect the power chamber with a hydraulic pump when the input shaft is moved forward, whereas the power chamber is switched over to communicating with a reservoir when the input shaft is moved backward, the control valve lifting quantity, this is, the input shaft shifting quantity must be increased to secure a sufficient passage area during operation. However, the disadvantage is that, because a large input shaft shifting quantity will be required until the stationary input shaft is moved forward to cause the switching of the passage of the control valve by increasing the input shaft shifting quantity, the loss stroke of the input shaft in its initial stage of operation tends to become larger.